The present invention relates to a polishing pad for use in chemical mechanical planarization applications. More particularly, the present invention relates to a method of joining sections of polishing pad for use in the chemical mechanical planarization or polishing of semiconductor wafers.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual integrated circuit chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. The need for a precise image projection is accentuated with the current drive toward smaller, more complex integrated circuit designs. Semiconductor wafers are also commonly constructed in layers, where a portion of a circuit is etched on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on the wafer, an oxide layer is put down that allows the vias to pass through the oxide layer while covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer as it is constructed. These imperfections are preferably smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad that is moving in the plane of the wafer surface to be planarized. A polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer.
The polishing pads commonly used in this process include belt-type pads and rotary-type pads. A belt-type pad typically consists of one or more sections of material that are formed into a belt by laminating or bonding the sections to each other and/or to a support structure. The joining of multiple sections of material requires the formation of joints where the sections meet. In a typical joint, there is a small space left between the two sections. These joints are subject to stresses that can cause the sections to delaminate. Delamination of the sections can result in a complete failure of the joint. The failure rate of the joints is increased as the slurry used with the pad seeps into the space between the sections.
A rotary-type pad typically consists of one or more sections of material that are joined together to form a pad. The pad is attached to a rotary machine that rotates the pad to polish a wafer. The joints in this type of pad are also formed by laminating or bonding the sections to each other and/or to a support structure and also subject to the same failure as the belt type pad. A polishing pad that overcomes these deficiencies is needed.
According to one aspect of the invention, a first section of polishing pad is welded to a second section of polishing pad to form a joint that is not susceptible to infiltration of a slurry and is resistant to delamination failure. The first section of polishing pad preferably overlaps the second portion of polishing pad to further increase the integrity of the joint. The combination of overlapping and welding the sections effectively seals the joint and prevents slurry from penetrating the joint. According to other aspects of the invention the sections of polishing pad can be welded in configurations where they are butted to or interlocked with one another. These configurations also effectively seal the joint and prevent slurry from penetrating the joint. Also, the sections of the polishing pad can comprise one or more portions materials or cushioning materials.